I've stayed in Lanzarote and Tenerife in July and August, without air conditioning. Lanzarote was fine - it was windy and the evenings felt a tiny bit chilly after a day in the hot sun, Fuerteventura would be pretty much the same, they are both "windy" islands. Tenerife was little too hot in the evenings in August, but then it's not as windy in the summer there as it is in Lanza/Fuerte.
It's possible to get by without it in the Canary Islands, but I wouldn't book anywhere in the Med (Greece/Spain/Turkey etc) without air conditioning.